1. Field of the Invention
The present invention relates to an electrical insulation coated metallic wire consisting of a releasing layer coated on a metallic wire with an insulating layer superposed on the releasing layer. The insulating layer formed on the releasing layer by coating and baking an insulating varnish on the releasing layer may easily be stripped from the metallic wire. The present electrical insulation coated metallic wire has excellent characteristics with respect to its thermal, mechanical, electrical and chemical properties, and can be used as an insulated conductive wire or an insulated resistance wire, the former using a conductor as the metallic wire and the latter using an electric-resistive substance as the metallic wire.
2. Description of the Prior Art
In conventional electrical insulation coated metallic wires which have hitherto been prepared, when the insulating layer is formed by coating and baking an insulating varnish on a metallic wire, the insulating layer can be stripped from the wire only with great difficulty. It has been considered that easy stripping as is achieved with the present invention would be impossible.
With respect to insulated conductive wires, particularly to those other than magnet wires, which are used for the wiring in electronic equipment or the like, it is an indispensable requirement that the insulating layer of the wire be easily stripped by means of simple tools to expose the conductor, for example, when the wires are to be connected together at their ends. For such use, insulation coated wires prepared by using an extrudable material such as polyethylene, polyvinyl chloride, polyamide, fluorinated ethylene-propylene copolymer, etc., have hitherto been utilized. In these coated wires prepared by the extrusion coating method, it has become necessary in recent years to reduce the thickness of the coating layer for the purpose of decreasing the space factor of the wire and to improve the thermal, electrical, mechanical and chemical characteristics thereof for the purpose of increasing the reliability.
More specifically, with respect to insulated wires for use in wiring the interior of electronic equipment (for example wires for use in wiring a computer, a communication control unit, etc.) among the various properties of such insulated wires, a reduction of the space factor thereof has become very important, especially when such electronic equipment include transistor systems, IC systems or LSI systems. Thus, a reduction in both the diameter of the conductor and the thickness of the insulating layer is required. Further, an appropriate impedance matching between the circuit and the insulated wire has also become important, and in particular, it has become necessary to reduce the impedance. In this case, in order to lower the characteristic impedance of insulated wires, it is important to thin the insulating layer of the wire. Moreover, together with the need to thin the insulating layer of insulated wires, another requirement has been to improve the thermal, mechanical and electrical characteristics of the insulated wires for the purpose of increasing further the reliability thereof.
In uses of insulated wires in electronic equipment such as computers, the cost proportion of the insulated wires for wiring the interior of the computer apparatus is about 0.7% of the total cost of the hardware of the computer, and it is believed that the cost proportion will be reduced to about 0.5-0.4%. Thus, the proportion is extremely small.
However, although computer manufactures attach the greatest significance to the reduction of the cost for wiring, the second-most important objective is the elimination of any miss-wiring, and an improvement in the reliability of the insulated wires and the like. Recently, automatic wiring systems have widely been adopted for the purpose of reducing the cost of wiring and for eliminating any miss-wiring, and at present about 80% of wiring operations have been accomplished by means of wiring apparatus. However, the mechanical damage imparted to insulated wires is great. As a result, not only is improvement with respect to the initial reliability of the wired insulated wires difficult to attain, but also it is difficult to maintain the reliability over a period of time (due to the poor mechanical strength of the insulating layer of the insulated wires). Further with respect to the use of such automatic wiring machines, the same drawbacks as noted above apply to other equipment which require wiring of the interior thereof in addition to the above mentioned computers.
Another wiring problem occurs, for example, with respect to insulated wires used for wire harnesses, e.g., wire harnesses used in automobiles. In making automobiles, it has hitherto been stressed to make as small as possible the devices which are used therein, for the purpose of reducing the weight thereof and for enlarging the area in the automobile which may efficiently be utilized by the passengers. Moreover, the necessary purification of the exhaust gases is generally done by adding additional devices to the conventional automobile. In the wiring used in an air purification device, heat resistance occassionally is required, for example, due to temperatures therein of higher than 200.degree. C. Under such circumstances, it has become necessary to not only reduce the space factor, but also to improve the thermal resistance of on the insulated wires used in the wiring of such devices for automobiles. In order to satisfy such needs, it becomes necessary by all means to make as small as possible the diameter of the core wire of the insulated wires for wire harnesses which have been used up to the present, and also to thin the insulating layer.
With respect to heat resistance, difficult problems exist in conventional insulated wires having a conventional wire diameter and a conventional insulating film thickness since even such conventional insulated wires have poor resistance to heat at high temperatures, for example, temperatures higher than 200.degree. C.
Under such circumstances, it is a very difficult problem to improve the heat resistance of insulated wires with the simultaneous reduction of the thickness of the insulating layer. Moreover, a high safety is required in automobiles, and so it is inevitable that a high reliability is being required more and more. Accordingly, in order to fully satisfy such needs, it is necessary to improve the thermal, electrical, mechanical and chemical characteristics of the insulated wires. These problems are related more or less to other insulated wires for wire harness other than those used for automobiles.
Apart from the above, in the communication cables of appliances for prevention of fire disasters and the like, an improvement of in heat resistance of these cables has also become absolutely indispensable.
Prior to the present invention, the insulated wires which have been used for the wiring of apparatus and the like have been produced by extrusion. In the insulation coating method by means of extrusion, however, reduction of the thickness of the insulating layer is limited. Various methods have been investigated for the purpose of reducing the thickness of insulating layer in the extrusion coating. However, when the thickness of the insulating layer become less than 100 .mu., it becomes very difficult with present technology to continuously and economically manufacture such insulated wires by means of the extrusion coating method.
In addition, when the core wire has been made very slender, various problems occur in the extrusion coating method such as wire-snapping, etc. The insulating layer provided by extrusion coating by using conventional materials have functions of not only electrically insulating the conductor but also of augmenting the thermal and mechanical characteristics of the insulated wire owing to the thickness of the insulating layer. Therefore, even if thinning of the insulating layer is desired in the extrusion coating method, or even if the thinning of the layer is actually performed in the extrusion coating method to the extent as industrially possible at present, the maintenance of the thermal and mechanical characteristics of the obtained insulated wires becomes very difficult. Furthermore, if the necessary maintenance of the thermal and mechanical characteristics is contemplated by using any materials other than the conventional ones, the scope of the materials which may be selected for utilization in the extrusion coating method is very limited, i.e., since the materials to be coated must necessarily have theremo-plasticity, be molten and further the molten materials must be stable for a long period of time at the melting temperature thereof. Accordingly, numerous factors with respect to the selection of the materials to be used exist, factors which depend upon the selectivity of the materials, the thermal characteristics (for example heat resistance, heat softening resistance, etc.), the mechanical characteristics (for example, abrasion resistance, etc.), the electrical characteristics (for example, characteristic impedance, etc.), the chemical characteristics, and so on. In addition, if such materials as having the highest thermal and mechanical characteristics of those which can satisfy the various conditions as mentioned above are used, the extruding conditions on the extrusion of the selected materials will naturally have to be more severe than in the case of the extrusion of conventional materials, and thus, it become still more difficult to contemplate a reduction in thickness of the insulating layer coated on the wires. For these reasons, it is impossible to actually manufacture insulated wires which satisfy the above-mentioned severe requirements by the extrusion coating method practised in this field, i.e., in view of the manufacture itself of the insulated wires and of the various characteristics themselves of the resulting insulated wires.
A second method for the manufacture of insulated wires is known. This method involved coating and baking an insulation varnish on a conductor. The insulated wires which are prepared by coating and baking the insulating varnish on the wire are used only in the field of so-called magnet wires. In this field, it is necessary to reduce the thickness of the insulating layer as much as possible, and further, extremely high characteristics are at the same time required concerning on the thermal, mechanical, electrical and chemical properties of the insulated wires. In addition, uniformity of the characteristics of the insulating layer is essential. Moreover, unlike insulated wires for use in wiring of electronic apparatus, in the field of magnet wires a close adhesion and a high coherence between the insulating layer and the conductor are absolutely necessary because of the natural characteristics of the magnet wires, and thus any easy stripping of the insulating layer from the conductor is detrimental and must be eliminated. Therefore, in testing of magnet wires, adhesion of the insulating layer determined by twisting of the wires and the coherence of the insulating layer to the conductor after sudden snapping of the wires are important factors.
With magnet wires, even in those which are said to be poor in coherence between the insulating layer and the conductor, the insulating layer will slightly rise up (or peel off) from the conductor only after severe testing as mentioned above, or in other words, only after such severe mechanical stresses have been imparted to the wires to be tested that the wires after being subjected to the testing can no longer be used as insulated wires, and of course the insulating layer of these magnet wires is never stripped easily from the conductor by means of simple tools even after the importing of mechanical stresses.
As will be apparent from the above explanation, the insulated wires for use in wiring of electronic equipment which are manufactured by the conventional extrusion coating method and the wires used in magnets, are quite different from each other with respect to (1) the thickness of the insulating layer, (2) the materials to be used, (3) the strippability and (4) the manufacturing methods themselves. Moreover, these two kinds of wires are also different from each other with respect to the costs, characteristics and fields of use. Under these circumstances, previous investigation has not hitherto taken into consideration concerning the use of magnet wires in the wiring of electronic equipment or even the possibility thereof. Accordingly, for the purpose of increasing, for example, the heat resistance of the insulated wires for the use in wiring of electronic equipment, a method for imparting a cross-linking to the polyethylene or polyvinyl chloride layer coated on the wire by means of a peroxide or of an electron-beam radiation has mainly been investigated.
However, the heat resistance of the thus treated wires still is not comparable to that of the insulating layer of magnet wires, and moreover, these wires are manufactured by the extrusion coating method as mentioned above and so the difficult problems on the thinning of the insulating layer are still not solved.
Being well familiar with the problems which must be solved in the field of the insulated wires, for example, those used in wiring of electronic equipment, manufactured by the conventional extrusion coating method and with various elements required of conventional insulated wires, the inventors have unexpectedly found that the difficult problems that have hitherto been involved in the field of insulated wires, particularly for use in wiring of electronic equipment can successfully be solved and the various requirements in this technical field can be achieved by utilizing the insulating materials of magnet wires and by adopting the manufacturing methods for these magnet wires in the field of insulated wires. Such utilization and adoption have not been taught by anyone up to the present.
Another filed in which the present invention deals is wires, which are termed insulated resistance wires. These wires have as the metallic wire an electric-resistive substance, and thus are different in function from the insulated conductive wires as explained hereinbefore.
The uses of such resistance wires widely vary, for example, they can be used in resistors, heat generators, thermo-coupler, etc., and according to the uses thereof, the structure, shape, wire diameter and characteristics of the wires also widely vary.
With respect to the structure of resistance wires, some naked resistance wires may be used as such, and on the other hand the wires may be coated for insulation.
With respect to the insulation of the resistance wires, various kinds of insulating materials and various insulation coating methods may be utilized. With respect to the shapes of the resistance wires, the wires may be used in the form of a rolled coil, or of a twisted wire or the like. Regarding the wire diameter, the diameter may be large such as several milli-meters or more, or may be small such as several ten milli-microns or less. With respect to the characteristics, various electrical, thermal, mechanical and chemical characteristics and so on are required, depending upon the uses of the resistance wires.
As mentioned above, the resistance wires have various uses, and among them, insulated resistance wires which are manufactured by coating and baking an insulating varnish on a resistance wire are utilized in applications wherein reduction of the space factor and electrical, thermal, mechanical and chemical characteristics are specifically required.
However, the insulated resistance wires which are prepared by coating and baking the insulating varnish have some difficulties such that when the insulating layer of the end of the said wire is to be stripped, the layer can be stripped only with difficulty by means of simple tools and the like. In view of such problems it has become important to manufacture insulated resistance wires in which the stripping of the insulating layer in their end parts is easy and which have a small space factor and excellent electrical, thermal, mechanical and chemical characteristics.
One example of such insulated resistance wires is in a thermocouple which is used for the measurement of temperature. In this case, as the insulating layer, in general, knitted glass yarns, extruded coating layer made of polyvinyl chloride are used. In some particular cases, insulated resistance wires which are prepared by coating and baking insulating varnish are used.
The thermo-couple is one which indicates a temperature by means of the thermo-electromotive force thereof, and so when it is connected to any other metal, an erroneous result will occur in the measurement. The deterisiation of the thermo-couple due to air or a gas under a high temperature results in variation of the electromotive force thereof or wire-snapping, etc. Accordingly, it is necessary that the thermo-couple is completely insulated, and it also is an indispensable matter that the insulating materials for the insulation must be thermally and chemically stable. In addition, severe mechanical stresses are imparted to the thermo-couple in some applications wherein the thermo-couple is used, and in such cases it cannot be permitted that the insulation of the thermo-couple be damaged due to the mechanical stresses. Thus, it is necessary that the insulating layer have a sufficient mechanical strength. In the conventional technical arts, the thermo-couple has hitherto been used for the measurement of temperature of various kinds of substances. In recent years, close temperature control has become required with the development of different industries, and it has become necessary to determine the temperature of very small substances which cannot be measured by means of conventional thermo-couples. For this reason, a reduction in the wire diameter of the thermo-couple and a reduction in the thickness of the insulating layer coated on the wire of the thermo-couple have become required so that the termo-couple may easily be inserted in such small substances to be measured. In conjunction with the need to reduce the thickness of the insulating layer, however, any decrease in the thermal, electrical, chemical and mechanical characteristics of the thermo-couple is not permissible in view of the above mentioned circumstances.
In cases where the thermo-couple is used for the measurement of the temperature of an atomic pile or of apparatus near an atomic pile, it is an indispensable condition that the thermo-couple to be used therefor have a resistance against radiant rays.
Anyhow, it is required to manufacture insulated thermo-couples in which the space factor is reduced and which have excellent thermal, electrical, chemical and mechanical characteristics. If these conditions are fully satisfied, the thermo-couples are complete. However, it is further required for the thermo-couples that the insulating layer of the insulated resistance wires can easily be stripped by means of simple tools so that the end part stripping can be easy.
As another example is a resistance wire which is used in the resistor of an electronic apparatus circuit.
In recent years, the sizes of electronic apparatus have noticeably been made smaller and smaller, and it has become desired to decrease the sizes of the resistors too with the increased use of a transistor system, an IC system or a LSI system in the circuit of the apparatus. Accordingly, a reduction of the diameter of the wire and the thinning of the insulating layer are required in the resistance wires used. Almost all of the resistors are ones which are prepared by closely rolling an insulated resistance wire in the form of a coil. In case an accurate resistance value is required, it is necessary to impart a heat treatment to the resulting resistor for the purpose of eliminating any strain which may occur during the rolling of the resistance wire in the coil form. For this purpose, it is necessary that the insulating layer be thermally stable.
In addition, it also is important that the strippability of the insulating layer from the core resistance wire is good whereby the insulating layer may easily be stripped at the end part of the wire when the wire is worked further.
As mentioned above, the matters which are required in the insulated resistance wires are as follows: The thinning of the thickness of the insulating layer is attained for the purpose of reducing the space factor, and at the same time the thin insulating layer has at least one or more excellent thermal, mechanical, electrical and chemical characteristics, and further the insulating layer may easily be stripped by means of simple tools.
Now, under such circumstances, insulated resistance wires which have been manufactured by coating and baking an insulating varnish on a resistance wire have been utilized at present. As the other insulation coating methods other than coating and baking method, there may be mentioned, for example, a knitted glass yarn coating method, a vinyl resin extrusion coating method and the like. In the former glass yarn method, however, reduction of the space factor cannot be expected, and in the latter resin extrusion method, the insulating layer cannot be used at a higher temperature of about 200.degree. C, and at about 150.degree. C or so, the resin is softened. Thus, these two methods do not comply with the above-mentioned requirements.
The insulating method for coating and baking an insulating varnish has been widely utilized in the field of insulated wires which are called as magnet wires. In the magnet wires, it is necessary to thin the thickness of the insulating layer as thin as possible, and further extremely high characteristics are required with respect to all of the thermal, mechanical, electrical and chemical properties thereof. These characteristics are the same as those which are required at present with insulated resistance wires, and it is not too much to say that in the present situation, only the insulated resistance wires which are manufactured by the coating and baking method of the insulating varnish have thin insulating layer which show excellent thermal, mechanical, electrical and chemical characteristics, or, in other words, any other wires which may have such thin insulating layers cannot be manufactured by means of any other conventional methods other than the above-mentioned coating and baking method. Because of this fact, the insulated resistance wires which are manufactured by coating and baking the insulating varnish on the core resistance wire are utilized in the field that the reduced space factor and the excellent thermal, mechanical, electrical and chemical characteristics are required.
However, in the insulated resistance wires which are manufactured by the coating and baking method of the insulating varnish, the insulating layer cannot easily be stripped. Accordingly, when the end parts of the wires are treated for stripping the coated layer, the insulating layer is removed by shaving or firing the same, or by decomposing the same, with chemical agents. Although such troublesome treatments are required for the removing of the insulating layers, the insulated resistance wires which are prepared by coating and baking the insulating varnish have been utilized at present. This is because, as mentioned above, any other wires which are prepared by other insulation coating methods do not satisfy the necessary factors which are required for the insulated resistance wires.
Under such circumstances, the insulated resistance wires which are prepared by coating and baking the insulating varnish have been utilized up to the present, but any improvement has not as yet been attained on the strippability of the insulating layer when the layer on the resistance wire is to be removed at its end part. Any investigation on the strippability of the insulating layer from the resistance wire by means of simple tools has not been performed or has not even been taken into consideration.
Having been well familiar with the matters which have been required up to the present on the insulated resistance wires, the inventors have found that manufacture of improved insulating resistance wires can be achieved by coating with an insulating varnish by means of a coating and baking method. In the insulated resistance wires according to the present invention, the insulating layer, may easily be stripped by means of simple tools. Such good strippability of the insulating layer has hitherto been considered impossible in the conventional technical arts, and has not even been taken into consideration.